This application is based upon a Japanese patent application, serial number 2000-093726, entitled xe2x80x9cPower system For Running Vehiclexe2x80x9d, of Ookoshi et al., filed on Mar. 30, 2000, Japanese patent applications, serial numbers 2000-128741, 2000-128742 and 2000-128743 entitled xe2x80x9cPower system For Running Vehiclexe2x80x9d, of Shimoura, Ookoshi et al., filed on Apr. 28, 2000, a Japanese patent application, serial number 2000-209284, entitled xe2x80x9cPower system For Running Vehiclexe2x80x9d, of Okuda et al., filed on Jul. 11, 2000, a Japanese patent application, serial number 2000-228688, entitled xe2x80x9cPower system For Running Vehicle and State of Charge Estimating Method for the Systemxe2x80x9d, of Ookoshi et al., filed on Jul. 28, 2000, a Japanese patent application, serial number 2000-231620, entitled xe2x80x9cPower system For Running Vehiclexe2x80x9d, of Okuda et al., filed on Jul. 31, 2000, and a Japanese patent application, serial number 2000-231621, entitled xe2x80x9cSecondary battery For Running Vehiclexe2x80x9d, of Maeda et al., filed on Jul. 31, 2000.
The present application relates to a 42V power system and a state of charge estimating method, and in particular relates to a 42V power system which is mounted on a vehicle and which can receive power supplied from a generator, and a state of charge estimating method for estimating a state of charge of the 42V power system.
Conventionally, a power system where a 12V system lead-acid battery is housed (hereinafter, referred to as 14V system) has been used in an automobile. In the 14V system, current is supplied (discharged) from the 12V system lead-acid battery to a vehicle starting device (starter motor), and after an engine starts, current is always supplied (charged) to the 12V system lead-acid battery from the generator operated by rotating force of the engine. However, the energy at a time of deceleration of the automobile is consumed as heat.
In recent years, instead of the 12V system lead-acid battery, a new type power system where a 36V system lead-acid battery is mounted (hereinafter, referred to as 42V system) has been proposed. In the 42V system, it has been made possible to use a high power motor generator as a vehicle starting device for starting the engine of the vehicle. For this reason, the energy which had conventionally been consumed as heat at the time of deceleration of the automobile is converted to electric energy by the motor generator to be supplied (charged) to the 36V system lead-acid battery as regenerative energy. According to the new power system, energy efficiency is increased so that fuel consumption in the automobile can be improved.
As shown in FIG. 13, in the 36V system lead-acid battery, a mono-block container having 12 cell chambers partitioned in a matrix of 2 rows and 9 columns is used. Unit cells of 2V lead-acid battery are accommodated in the respective cell chambers. The respective unit cells are connected serially by inter-cell connecting members 19 for connecting adjacent cell chambers in the order of the first row and the first column, the first row and the second column, the first row and the third column, the first row and the fourth column, the first row and the fifth column, the first row and the sixth column, the first row and the seventh column, the first row and the eighth column, the first row and the ninth column, the second row and the ninth column, the second row and the eighth column, the second row and the seventh column, the second row and the sixth column, the second row and the fifth column, the second row and the fourth column, the second row and the third column, the second row and the second column, and the second row and the first column. Also, the 36V system lead-acid battery is provided at the cell chambers which are respectively defined by the first row and the first column and the second row and the first column with external output terminals (positive external terminal 16 and negative external terminal 17).
However, the motor generator used for the 42V system generates a high power of 3 to 4 kW, and the current value at a regeneration time thereof reaches 40 to 80 A (corresponding to 2 to 4 CA) . In the lead-acid battery, when the charged rate reaches a current value of 1 CA or more, a decomposition reaction of water which is a sub-reaction at a time of charging is accelerated so that the charging efficiency is reduced, thereby affecting the life of the battery adversely. Therefore, it is difficult to allow such large current charging in a conventional lead-acid battery.
In order to solve this problem, there has been a proposal where control is performed so as to achieve a constant voltage charge within a range where the sub-reaction does not occur. However, the charge reaches the constant voltage region rapidly, loss of the regenerative energy increases. Also, in a case that a large current charging is allowed, there occurs a drawback in that the temperature of the lead-acid battery ascends and the life of the storage battery may be decreased in an assumption that the battery is mounted in the engine room (atmospheric temperature of 60xc2x0 C.) of an automobile.
It is desirable that the state of charge of the lead-acid battery is controlled within a range of 60% to 80%. In order to control the state of charge of the battery, a method for measuring an open circuit voltage is mainly employed conventionally. However, such an error factor that a long time is required until the open circuit voltage of the lead-acid battery is made stable is large, so that a sufficient control accuracy of the state of charge in the lead-acid battery could not have been achieved.
Further, in the structure of the lead-acid battery shown in FIG. 13, the external terminals are provided at the cell chambers of the first row and the first column and the second row and the first column. Therefore, there is a problem in that, since the distance between the external terminals are made close to each other to be shortened, leakage current becomes easy to flow between the 36V terminals. Further, when the 36V lead-acid battery is connected in the power system (42V system), erroneous connection may occur between a plus cable and a minus cable.
In view of the above circumstances, a first object of the present invention is to provide a power system where energy generated at a time of deceleration of a running vehicle such as an automobile can be received as regenerative energy sufficiently and safely.
Also, a second object of the present invention is to provide a state of charge estimating method where a control accuracy of the state of charge in a power system is high.
In order to achieve the above objects, according to the present invention, there is provided a 42V power system which is mounted on a vehicle and which can receive electrical power supplied from a generator, comprising: an aqueous solution system secondary battery group where a plurality of aqueous solution system cells are connected; and a non-aqueous solution system secondary battery group which is connected to the aqueous solution system secondary battery group in parallel, which has a group battery capacity smaller than that of the aqueous solution system secondary battery group, and where a plurality of non-aqueous solution system cells are connected.
In the present invention, the aqueous solution system secondary battery group where its battery capacity is large but its capacity receiving regenerated power from a generator is small and the non-aqueous solution system secondary battery group where its battery capacity is small but its capacity receiving regenerated power from a generator is large are connected to each other in parallel. At a braking time of a vehicle, power of a large current regenerated from the generator is charged into the non-aqueous solution system secondary battery group and the aqueous solution system secondary battery group. Since the regenerated power receiving capacity of the non-aqueous solution system secondary battery group is larger than that of the aqueous solution system secondary battery group, more power (electric energy) is accepted in the non-aqueous solution system secondary battery group. Since the braking time of the vehicle is short, the battery capacity of the non-aqueous system secondary battery group can be made smaller than that of the aqueous solution system secondary battery group. Since the non-aqueous solution system secondary battery group and the aqueous solution system secondary battery group are connected to each other in parallel, the power which has been once accepted in the non-aqueous solution system is supplied to the aqueous solution system secondary battery group.
According to the present invention, since the regenerated energy at the braking time of the vehicle can be accepted (charged) efficiently by combining the non-aqueous solution system secondary battery group and the aqueous solution system secondary battery system to each other, a power system with a high energy efficiency can be realized.
In this case, when the charging voltage of the non-aqueous solution system secondary battery group is set to 4.2V/cell or less, the temperature raising can be suppressed at a charging time of the non-aqueous unit cells, so that the safety of the power system can be secured. Also, there is provided a state of charge estimating method which estimates a state of charge of a power system which comprising a flow divider diving current so as to maintain the states of charge of the aqueous solution system secondary battery group and the non-aqueous solution system secondary battery group in the same level and where a charging/discharging circuit of the aqueous solution system secondary battery group and a charging/discharging circuit of the non-aqueous solution system secondary battery are connected to each other through the flow divider, wherein the state of charge of the aqueous solution system secondary battery group is estimated by detecting the state of charge of the non-aqueous solution system secondary battery group, the state of charge of the aqueous solution system secondary battery group can be estimated with a high accuracy on the basis of the state of charge of the non-aqueous solution system secondary battery group. At this time, it is preferable that the power system is provided with a battery controller which controls the state of charge of the non-aqueous solution system secondary battery group.
The present invention will become more apparent by referring to preferable embodiments described below.